The present invention relates to a wireless communication system and a wireless communication apparatus, and more particularly, to a wireless communication system and a wireless communication apparatus that are characterized in a method of returning to an active state from a sleep state in an ad-hoc network.
At present, a standard specification to achieve a high-speed wireless personal area network (PAN) is defined in IEEE802. 15. 3 and is being recognized as one of the high-speed wireless communication systems. For example, International Publication WO 2004/071020 pamphlet defines a method by which one activation is carried out in a plurality of superframe periods as a power-save mode, and a wireless communication apparatus (terminal) other than a control station (PNC) switches back and forth between two operating states of a sleep state and an active state as necessary, thereby enabling low power consumption operation.
That is, there is defined a method by which the wireless communication apparatus that operates with low power consumption continues the sleep state over several superframes and then transitions to the active state only for one superframe, exchanging data with the control station and other wireless communication apparatuses in this timing. That is, since the control station that does not enter the sleep state receives beacon signals at regular time intervals, the adjacent wireless communication apparatuses (terminals) carry out communication in synchronization with the beacon signals.
According to Japanese Patent Application Laid-Open No. 2002-64501 by the assignee of the invention, there is disclosed a technology that a wireless communication apparatus in a power-save mode informs the control station about the presence of other wireless communication apparatuses existing in the network. In the technology, there is shown a wireless communication method of informing the control station during a transmission activation period about the operating status of terminal stations that have been recognized during a reception activation period by setting two periods of a first period for reception and a second period for transmission.
Further, in recent years, there has been developed a method that adjacent wireless communication apparatuses operate in an autonomous distributed manner without a control station and constitute an ad-hoc network. Advantageously, such a network structure negates the need for the process of selecting a control station and simplifies the processing of entry into the network. In this case, due to no control station, it is difficult to define the power-save mode defined in the above-mentioned IEEE802. 15. 3; however, similar low power consumption operation is defined as a “hibernation mode.”
In the ad-hoc network, there has been a problem that though each wireless communication apparatus transmits a beacon signal, a wireless communication apparatus cannot accurately grasp its own beacon transmission position with reference to the beacon signals of other wireless communication apparatuses, depending on the beacon transmission position of the wireless communication apparatus in the hibernation mode.
Further, according to a transmission control method described in the Japanese Patent Application Laid-Open No. 2002-64501, a wireless communication apparatus in the power-save mode (also referred to as a sleep mode) requires setting the two periods of the first period for reception and the second period for transmission; therefore, the wireless communication apparatus cannot operate without an instruction or a request for the settings from the control station.
In a past communication system having a control station, a terminal station in the power-save mode has achieved synchronization with signals from the control station that always transmits signals. However, in the ad-hoc network, there has been a problem that each communication station cannot enter the power-save mode because due to no control station, it cannot specify which communication station to achieve synchronization with.
Further, in the ad-hoc network, there has been a problem that since each synchronization between adjacent wireless communication apparatuses is achieved for communication, a wireless communication apparatus cannot specify transmission timing of its own beacon signal unless the wireless communication apparatus receives specified beacon signals from adjacent wireless communication apparatuses.
Further, there has been a problem that the wireless communication apparatus cannot grasp the transmission position of its own beacon signal unless the wireless communication apparatus receives beacon signals from adjacent wireless communication apparatuses prior to the own transmission beacon signal position.
Furthermore, there has been a problem that in a wireless communication system in which the transmission position of a beacon signal is arranged at the head of a superframe period, the wireless communication apparatus cannot grasp the presence of adjacent wireless communication apparatuses, immediately after the wireless communication apparatus in the hibernation mode transitions to an active state.
Furthermore, there has been a problem that since the wireless communication apparatus has not received beacon signals from adjacent wireless communication apparatuses immediately after the wireless communication apparatus transitions from a sleep state to an active state, the wireless communication apparatus cannot exchange the presence and operating states of adjacent wireless communication apparatuses, using a transmission beacon signal.
The present invention has been made in view of the foregoing problems which the past wireless communication system and wireless communication apparatus have, and it is desirable to provide new and improved wireless communication system and wireless communication apparatus capable of specifying a transmission position of an accurate beacon signal at the time of transitioning from the sleep state to the active state in the ad-hoc network.
Furthermore, it is desirable to provide new and improved wireless communication system and wireless communication apparatus capable of transmitting an accurate beacon signal including the presence of adjacent wireless communication apparatuses when the wireless communication apparatus in the hibernation mode transitions from the sleep state to the active state.